Using ecological context to interpret spatiotemporal variation in natural selection

Abstract

Spatiotemporal variation in natural selection is expected, but difficult to estimate. Pollinator‐mediated selection on floral traits provides a good system for understanding and linking variation in selection to differences in ecological context. We studied pollinator‐mediated selection in five populations of Dalechampia scandens (Euphorbiaceae) in Costa Rica and Mexico. Using a nonlinear path‐analytical approach, we assessed several functional components of selection, and linked variation in pollinator‐mediated selection across time and space to variation in pollinator assemblages. After correcting for estimation error, we detected moderate variation in net selection on two out of four blossom traits. Both the opportunity for selection and the mean strength of selection decreased with increasing reliability of cross‐pollination. Selection for pollinator attraction was consistently positive and stronger on advertisement than reward traits. Selection on traits affecting pollen transfer from the pollinator to the stigmas was strong only when cross‐pollination was unreliable and there was a mismatch between pollinator and blossom size. These results illustrate how consideration of trait function and ecological context can facilitate both the detection and the causal understanding of spatiotemporal variation in natural selection.

Quantitative assessment of observed versus predicted responses to selection

“…2013; Albertsen et al. 2021). Finally, we note that the asymmetry is more pronounced on an arithmetic scale and is thus not restricted to the log‐scale we used.…”

“…2013; Albertsen et al. 2021). Additionally, the Dalechampia blossom is an integrated structure in which involucral‐bract size is phenotypically and genetically correlated with resin‐gland size (Armbruster 1991; Hansen et al.…”

Measuring, comparing and interpreting phenotypic selection on floral scent

“…For G. odoratissima , we assessed spatio‐temporal variation in selection on each compound through the approach of Albertsen et al (2021), in which the among‐dataset variation is computed aswhere is the variance of the selection‐gradient estimates among datasets, and is the sampling variance of each selection‐gradient estimate. In the current Bayesian framework, we used the variance of the posterior distribution as an estimate of the sampling variance (squared standard error).…”

Comparative reproductive ecology of two sisterAsarumspecies (Aristolochiaceae) in relation to the evolution of elongated floral appendage

“…Floral diversity has been largely interpreted as the historical outcome of pollinator-mediated selection since the time of Darwin (Harder & Johnson 2009;Ollerton et al 2011, but see Strauss & Whittall 2006). Floral traits are considered to be associated with multiple aspects of reproductive ecology, such as mating system, pollination efficiency and pollen dispersal distance (Galen & Stanton 1989;Anton et al 2013;Albertsen et al 2021). These reproductive characters often change concurrently (Waser 1983) and could together influence plant fitness (Gaudeul & Till-Bottraud 2004).…”

“…2013; Albertsen et al . 2021). These reproductive characters often change concurrently (Waser 1983) and could together influence plant fitness (Gaudeul & Till‐Bottraud 2004).…”